The Karvonen formula is used to calculate your target heart rate for exercise. It does this by factoring in both your maximum heart rate and your resting heart rate, producing a personalized training zone that reflects your actual cardiovascular fitness. This makes it more individualized than simpler methods that only use age.
How the Formula Works
The Karvonen formula centers on a concept called heart rate reserve, which is the difference between your maximum heart rate and your resting heart rate. That gap represents the range your heart has available to work harder during exercise. Someone with a resting heart rate of 60 beats per minute (bpm) and a max of 190 bpm has a reserve of 130 beats to draw from. Someone the same age with a resting rate of 80 bpm has a smaller reserve of 110 beats, and their target training zones should reflect that difference.
The formula itself has three steps:
- Step 1: Find your heart rate reserve (HRR) by subtracting your resting heart rate from your maximum heart rate. HRR = Max HR − Resting HR.
- Step 2: Multiply your HRR by the exercise intensity percentage you’re aiming for (for example, 0.50 for 50%).
- Step 3: Add your resting heart rate back to that number. Target HR = (HRR × intensity%) + Resting HR.
That final step, adding the resting heart rate back in, is what distinguishes the Karvonen method from simply taking a percentage of your max heart rate. It anchors the calculation to your personal baseline.
A Quick Example
Say you’re 40 years old with a resting heart rate of 65 bpm. Using the common estimate of 220 minus your age, your predicted max heart rate is 180 bpm. Your heart rate reserve is 180 − 65 = 115 bpm.
If you want to exercise at a moderate intensity of 45% to 55% of your heart rate reserve (a range the American College of Sports Medicine recommends for improving cardiovascular health and body composition), the math looks like this:
- Low end: (115 × 0.45) + 65 = 117 bpm
- High end: (115 × 0.55) + 65 = 128 bpm
Your target zone for moderate exercise would be roughly 117 to 128 bpm. For a more vigorous session at 60% to 80% of reserve, the range shifts to about 134 to 157 bpm.
Why It’s More Personalized Than Simpler Methods
The most basic way to estimate a training zone is to take a straight percentage of your age-predicted max heart rate (220 minus age). That approach treats everyone the same age as identical, ignoring fitness level entirely. A well-trained runner and a sedentary office worker who are both 35 would get the same target heart rate, even though their cardiovascular systems are in very different shape.
The Karvonen formula corrects for this by incorporating resting heart rate, which is a rough but useful proxy for fitness. Fitter people tend to have lower resting heart rates because their hearts pump more blood per beat. By building that number into the equation, the formula produces a higher target for someone who is already fit and a lower one for someone just starting out. Cardiac rehab programs rely on this approach for exactly that reason: it scales to the individual.
The 220-minus-age estimate for maximum heart rate also carries its own error. Research published in the International Journal of Exercise Science found this equation has a standard deviation of 10 to 12 bpm, and it tends to overestimate max heart rate in younger adults while underestimating it in older adults. If you have access to an actual measured max heart rate from a supervised exercise test, plugging that into the Karvonen formula instead of the age-based estimate makes the result considerably more reliable.
How to Measure Your Resting Heart Rate
The accuracy of the Karvonen formula depends heavily on getting a reliable resting heart rate. The standard protocol is simple: count your pulse for a full 60 seconds first thing in the morning, before you get out of bed. Do this on several consecutive days and use the average. Caffeine, poor sleep, stress, and illness can all temporarily raise resting heart rate, so a multi-day average smooths out those fluctuations. A wrist-based heart rate monitor or fitness tracker that logs overnight data can also give you a reasonable number, though manual measurement remains the benchmark.
Common Intensity Ranges
The percentage you plug into the formula depends on your goal and fitness level. The ACSM guidelines map out the general zones when using heart rate reserve:
- Light intensity: 30% to 39% of HRR. Suitable for people who are very deconditioned or just beginning to exercise.
- Moderate intensity: 40% to 59% of HRR. This is the range most commonly recommended for general cardiovascular health. Research on aerobic exercise and body composition has used 45% to 55% of HRR with sessions of about 45 minutes, four times a week, and found meaningful improvements in cardiorespiratory fitness.
- Vigorous intensity: 60% to 89% of HRR. Used for more demanding training when a solid aerobic base is already in place.
Note that these percentages are lower than the equivalent percentages of max heart rate. Exercising at 45% of your heart rate reserve is roughly comparable to exercising at 65% of your max heart rate. The two scales don’t translate one-to-one, so it matters which method you’re using when interpreting a training recommendation.
Limitations With Certain Medications
Beta-blockers, commonly prescribed for high blood pressure and heart conditions, artificially lower both resting and maximum heart rate. This changes the math in the Karvonen formula in ways that can produce misleading results. A study in the European Journal of Preventive Cardiology tested the formula in heart attack patients taking beta-blockers and found the standard Karvonen calculation underestimated the appropriate training intensity in 40% of patients. Their prescribed heart rate targets were significantly lower than the intensity their bodies could actually handle safely, potentially leading to workouts too easy to produce meaningful cardiovascular benefit.
Researchers proposed a modified version of the formula using a higher intensity coefficient (0.80 of heart rate reserve plus resting heart rate) for this population, which brought the error rate down to just 5% of patients. If you take beta-blockers or other heart-rate-lowering medications, your training zones are best determined through a supervised exercise test rather than a formula alone.
When the Formula Is Most Useful
The Karvonen formula fills a practical middle ground. It’s more personalized than a flat percentage of max heart rate, but it doesn’t require expensive lab testing like measuring oxygen consumption or lactate thresholds. That makes it especially useful for people designing their own workout programs, personal trainers setting intensity targets for clients, and cardiac rehab programs that need a quick, individualized starting point for patients recovering from heart events.
For competitive athletes chasing precise performance gains, lab-based thresholds will always be more accurate. But for the vast majority of people who just want to know whether they’re working hard enough (or too hard) during a run, bike ride, or group fitness class, the Karvonen formula provides a reliable, evidence-backed answer with nothing more than a clock and some simple arithmetic.